Weighty Decisions: Coffee Scales in Depth

In our pursuit of delicious coffee, baristas have constantly sought to understand and utilise all the information they can gather about the behaviour of their extractions. Managing the potentially wildly fluctuating variables surrounding fresh coffee and working them into a repeatable workflow has been key to capturing the subtleties of our increasingly finely tuned green coffee. With the popularisation of scales into espresso preparation over the past 5 or so years, there’s now even better tools and data available to dish out the goods. But just how good are your scales? And are you using this kit correctly? Scales aren’t just scales.

Choosing the right scales

There’s lots of options out there for measuring weight, but it can take a little research to figure out what’s right for you. The first thing to consider around your espresso setup is functionality. Will your portafilter fit on your scales? Will your scales fit on your drip tray? Will your scales survive a long black being accidentally tipped onto them?

The second thing to consider is the accuracy and precision of your scales. Now, you might be saying “Weight a second! If a scale reads 21g then there must be 21g on the scale, right?”.

Surprisingly though, more often than not, this isn’t the case. Cheap scales can provide inaccurate and imprecise readings which can become a pretty large issue when preparing espresso, especially considering the focus we have on consistency in specialty coffee. Here’s how to make sense of precision versus accuracy: An imprecise scale will deliver you a variety of results around your desired (or the calibrated) weight. It may read 20.6g one time and then 21.5g the next. An inaccurate scale will deliver you a result offset from the target. For example, you may put a verified weight on the scale of 500g and it will regularly read 510g. You can have combinations of these two situations as we’ve shown in the diagram below but in short, an imprecise scale will affect your consistency and an inaccurate scale will affect your recipe, impacting the strength and taste of all your espressos.

Beyond this core functionality, you should consider if there’s any extra features you need. Do you need an inbuilt timer? Would an auto-tare help? How durable is the scale for its use?

Acaia have rapidly become the scales of choice not only for us here at Five Senses but by coffee professionals and enthusiasts around the world. The big reason for this is that they deliver on not only both these accuracy and precision needs but are also boast a high quality, durable build. A minimalist design that would make apple jealous certainly doesn’t hurt either!

Setting up scales for your workstation

Your scales should know their place. The Acaia Pearl is great at weighing your dose into your portafilter and for pourover coffee. While it can be used to weigh your espresso shots, finding a stable position for it on the drip tray can sometimes be a little difficult. The Acaia Lunar, on the other hand, is designed specifically to live in this environment. It comfortably fits on any drip tray, has higher heat and water resistance than the Pearl and is even more accurate. The lunar also has some great features for espresso measurements such as auto-taring, auto-start and a timer that records the duration of an espresso shot (a must-have if your espresso machine doesn’t have shot timers).

Worth the weight?

A common reaction when training a barista who is new to specialty coffee is surprise that we recommend weighing every dose. We believe that with some good planning around bar setup and workflow, this practice can be implemented without compromising wait times and will ensure a significantly higher quality of beverage being served. Here’s a couple of neat workflow tips to help speed things up in a busy café environment:

Grind into dosing cups of equal weights. A small container that can sit on your grinder forks is perfect.

After removing your dosing cup from grinder place another one immediately into position and grind again while distributing your first dose into your portafilter.

With your loaded portafilter on the scales, check the dose and use a teaspoon to remove excess grounds.

Keep your grinder’s auto dosing setting as close to your recipe as possible (adjust every time your grind setting changes).

How accurate should I be with my dose?

For every extra gram in your dose your extraction time will typically increase by about 2 seconds. An increase to dose will also increase your TDS%, increasing the strength of the espresso and lower your extraction %, altering the taste of your espresso. So, how do you choose what your threshold for under or over your dose is acceptable? Each tenth of a gram you go over or under your dose (or yield) will have a small impact on strength, extraction time and extraction %. +/- 0.5g is a good starting point that should keep your extraction time within one second of your recipe, as well as keeping your extraction % within 0.3% of your target. However, the more precise you are, the more consistent your shots will be and in turn, the more predictable your coffee will taste.

Here’s a few examples of how these variables can shift your results:

Stop, calibrate, and listen.

High resolution scales such as the Acaia Pearl and Lunar require regular calibration. This is due to the weighing sensor being sensitive to not only weight, but also temperature, gravity, pressure, voltage etc. To ensure that your scale is calibrated to the environment it’s being used in, you should use a certified weight to calibrate it regularly. The more often you calibrate your scales, the more accurate and precise they will be. Acaia recommend weekly calibrations for their scales and have made the process to do this pretty quick and easy. The Acaia Lunar even comes with a 100g calibration weight included in the box.

Getting the most from your scales

Use your scales on a stable, level surface. Uneven surfaces will still give a steady reading, however, the weight shown will be less accurate than on an even surface (try weigh something on a level scale, then prop one side of the scale up and check the weight again). If you regularly use your scales on an unsteady bench, then you might notice the readings fluctuate. If moving your scales to a sturdier bench isn’t an option then you may want to lower the sensitivity of your scale. This will give you a steadier reading, but will lower the response time. See Acaia’s blog for details on this: Acaia University: Weighing sensor

High temperatures can affect the accuracy of readings and can damage scales, causing ‘drifting’. Acaia scales only use load cells with an accuracy of +/-2g when exposed to 100C water for 6 minutes. However, using the included heat mat when making pourover coffee will provide more accurate readings and keep the scales healthy. When not in use, storing your scales on their side will avoid constant pressure on the load cell and keep them calibrated for longer.

Overall scales are great and can help us achieve the cups of coffee we’re aiming for again and again but they’re only as good as their technology and how they’re dialled in. So remember to take care of your scales and they’ll take care of your espresso!

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